He swore he had nothing to do with wife’s death at sea. Now he’s expected to plead guilty to manslaughter.

Until now, Lewis Bennett faced a maximum of 17½ years in prison if convicted of killing his wife, who disappeared at sea during their honeymoon. Now there’s a chance he could get as little as 18 months.

Bennett, 41, is expected to plead guilty Monday to involuntary manslaughter in the death of his wife, Isabella Hellmann, a Delray Beach woman who was last seen alive when she and Bennett were spotted in the Bahamas aboard their 37-foot catamaran, Surf Into Summer.

Her body was never found, and she is presumed dead.

Exactly why Bennett, 41, is getting such a good deal is impossible to know until Monday. But the most likely explanation is that the prosecution, the defense and the victim’s family all agreed to settle for a certain outcome in a case that would be difficult to prove, according to defense attorneys who handle such challenging cases.

“You’ve got no body, you’ve got no great physical evidence, you’ve got a defendant who would probably take the witness stand to testify in his defense — and you’ve got to convince all 12 jurors in federal court,” said David S. Weinstein, a Miami-based defense attorney who formerly worked as both a federal and state prosecutor. “That’s a gamble.”

“Stack that against a conviction that will definitely put the defendant in prison, give the victim’s family some closure, stop him from collecting on life insurance and probably help to terminate his parental rights to the couple’s child,” Weinstein said. “They say a plea bargain means that both sides are unhappy but both sides can live with the outcome.”

The U.S. Attorney’s Office and the Federal Public Defender’s Office were not commenting Friday.

Mitchell Kitroser, an attorney who represents Hellmann’s family, said he and the family do not plan to comment on the case until they speak at Bennett’s sentencing.

Bennett initially told investigators that his wife, a real estate broker, disappeared on Mother’s Day 2017 when their vessel got into difficulty and sank near the Bahamas.

He said the catamaran was on auto pilot with his wife at the helm while he slept below deck. Bennett said he awoke when he heard a thud. The cabin flooded and the vessel sank and he never saw his wife again, he said.

A Coast Guard investigation cast doubt on his story. An expert found that the couple’s boat appeared to have suffered intentional damage on both sides of its hull that was not the result of a collision.

The expert said the damage came from inside the vessel, according to FBI records. Two escape hatches below the waterline were also found open, which caused the cabin to flood, investigators said, adding they believe the boat was “intentionally scuttled.”

They believe he then grabbed a backpack and hopped into a life raft. Stolen gold and silver coins were found in the raft when the Coast Guard rescued him. Investigators emphasized that Bennett apparently had time to save the coins, but not his wife, when the catamaran sank.

Bennett is locked up in the Federal Detention Center in downtown Miami, serving a seven-month federal sentence for transporting stolen goods — coins valued at more than $40,000. The coins were stolen from a vessel he worked on as a crew member in 2016 in St. Maarten.

Originally charged with second-degree murder in Hellman’s death, Bennett probably would have faced about 14 to 17½ years in federal prison if he had rolled the dice and been convicted after a jury trial.

Instead, he is expected to plead out to the lesser charge. He faces a maximum of eight years in prison but could get as little as 18 to 24 months, under federal sentencing guidelines.

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The anticipated plea agreement comes as prosecutors and Bennett’s assistant federal public defender were wrangling about what evidence could and couldn’t be used against him in his trial, court records show. The trial was tentatively scheduled for December.

The couple, who lived at Hellman’s condo in Delray Beach, had a baby daughter who was with relatives when Hellmann and Bennett went on their postponed honeymoon trip. Bennett later brought the girl, now 2, to live with his parents near Southampton, England.

The secret audio recordings were made by members of Hellman’s family who “placed two listening devices” in the master bedroom and living room of Hellmann’s condo shortly after her disappearance.

The family, who said Hellmann had always allowed them to go into her residence, later told investigators they had placed the devices there “to surreptitiously record activity within the home.” They did not tell law enforcement what they had done until just before the FBI searched the home, according to court records.

Bennett’s defense had argued that the recordings of Bennett could not legally be used against him in court. Prosecutors said they could because the family was not acting on behalf of law enforcement but had made the recordings for their own purposes. U.S. District Judge Federico Moreno had not yet ruled on whether those recordings could be used as evidence in the jury trial.

Weinstein, the former prosecutor who is not involved in the case, said he thinks the recordings would not have been usable at trial because Florida law requires both sides in a conversation to give consent for it be recorded — and the recordings were not made by law enforcement.

Prosecutors have said in court that Bennett had a motive to kill Hellmann because their relationship had grown rocky in the months before her death and they were arguing about their finances and child-rearing issues.

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The couple owed property taxes and also faced having their condo’s electricity cut off, according to court records. They also owed thousands of dollars for home renovations financed by Hellmann’s credit cards, for which they were making only minimum payments. They also disagreed on whether she should return to work because she wanted to stay home with their daughter.

Bennett wanted to move to Australia with their daughter, but Hellmann didn’t want to go, according to what friends told investigators.

Prosecutors also wanted to use evidence from Hellmann’s texts, emails and conversations she had with other people that indicated the marriage was in trouble. But the defense said those conversations did not tell the whole story and should not be used against Bennett, in part because of legal rules that protect communications between married couples.

In one text Hellmann had sent her husband about six months before she disappeared, she wrote: “You make me crazy shouting, yelling, swearing."

“I’m tired of you telling me I’m the MOST WORSE PERSON YOU EVER MET BEFORE, everything I do it’s WRONG … this is very pathetic Lewis,” she wrote in another text.

The manslaughter charge against Bennett accuses him of unlawfully killing Hellmann “without malice in the commission of a lawful act, without due caution and circumspection, which might produce death.” The criminal charge also alleges “gross negligence amounting to wanton and reckless disregard for human life.”